A preform generally comprises a tubular body that is closed, at a lower end, by a hemispherical bottom, and a neck, normally threaded, which extends the body from an upper end of the former. Most preforms are also provided with a collar that separates the neck from the body and that facilitates the handling of the preforms.
A cycle for manufacturing a container requires numerous operations for handling the preform from which the container is intended to be manufactured. From a bulk packing in a hopper (or a bowl, or any other bin), the preform is successively removed from the hopper, oriented (neck up or neck down), transferred to a heating unit (or oven), transported into it in a procession to undergo a thermal conditioning there, and then again transferred to a mold to be transformed there into a container by blow molding or stretch blow molding.
The transport speed of the preforms during such a cycle is not constant. In particular, the bulk packing of the preforms in the hopper or the bowl does not make it possible to feed the heating unit directly at its discharge. Consequently, between the hopper and the heating unit, an intermediate zone is provided where the preforms are temporarily accumulated to make possible a continuous feeding of the heating unit.
To perform this accumulation, a transport device is usually used that is equipped with an endless belt that carries the preforms along by rubbing, along a predetermined path (which can be linear at least in places).
The French patent FR 2 956 652 or its U.S. equivalent US 2012/312661 (SIDEL PARTICIPATIONS) describes a conveyor equipped with two endless belts, at least one of which has, in the area of an active part in contact with the preforms, a natural material consisting of leather.
This solution, which is actually currently used, is satisfactory to the extent that it makes it possible to perform the accumulation of the preforms effectively and without damaging them.
The rubbing against the preforms, however, causes, firstly, a rapid wear of the leather, which necessitates the frequent replacement of the belt.
Secondly, the rubbing produces a dust made of fine particles of leather that has a tendency to be deposited on the preforms and on the elements of the conveyor. Since the leather is a natural material, the resulting pollution is not hazardous, but it is not acceptable to allow the dust to accumulate on the conveyor, which consequently must undergo frequent cleanings.